Water, oil, and egg yolk to model how cell membranes form and function. The interaction shows how membranes act as barriers, keeping environments separate while allowing cells to exist and replicate.

1. Begin by explaining to students that all living things are made of cells, and each cell is surrounded by a membrane.
2. Pour 100 mL of water into a flask.
3. Add 25 mL of oil into the flask.
4. Shake the flask, then let it settle so the oil and water separate. Point out that they do not mix, similar to how a membrane forms a barrier.
5. Crack an egg into a small dish.
6. Use an eye dropper to collect some of the yolk.
7. Drop small amounts of the yolk into the oil-water mixture.
8. Observe how the yolk forms structures that resemble cell-like boundaries, illustrating how cell membranes create separation and stability.

egg yolk as emulsifier - Ssie Altalef:

📄 CELL MEMBRANES FROM EGGS (Page 16) - Sarah Groth: https://www.unco.edu/nhs/science/pdf/demos/2009_CSC_demos.pdf

• Use food coloring in the water to make the separation more visible.

• Wash hands thoroughly after handling raw egg.
• Clean surfaces and materials that come into contact with raw egg to prevent bacterial contamination (e.g., salmonella).
• Dispose of egg mixture properly—do not leave it sitting out in a classroom.

• Why is it important for cells to have membranes?
• How does the cell membrane protect the cell from its environment?
• Why do oil and water not mix, and how does this relate to membrane structure?
• What might happen if a cell did not have a membrane?
• How does this demonstration model the process of cells forming from preexisting cells?